The longdistance transmission of images is undertaken for different purposes. Two main purposes can be distinguished: the transmission of monochrome or color images with high transmission quality for reproduction in newspapers and magazines as the most important application, and the transmission of images and texts, often black and white in nature, for informative reasons, without high requirements for accurate reproduction and which has as its main object the transmission of documents in an office environment. The invention relates to apparatuses for the former purpose, which, however, does not prevent its possible use in the other main area if the quality which can be achieved by the invention is required even in this area. The following presentation will, however, mainly concentrate on apparatuses for the former purpose, i.e., apparatuses for the transmission of images. In the following it is assumed, for purposes of example only, that the image involved is a picture.
Previously known apparatuses of this type transmit a picture in a continuous synchronized fashion. The picture is scanned line by line in the transmitter and its varying levels of brightness give rise to a transmitted signal by means of lightsensitive elements. During the continuous scanning of the picture the signal is transmitted to the receiver via a telephone line, some other line, or wirelessly. The surface, normally a paper surface, on which the picture is to be created is scanned in the receiver in synchronization with the scanning of the original picture and a printing means gives the surface the blackening or the nuance of color which corresponds to the signal which is transmitted at that instant. Previously, an analog signal was used for the gray scale, but now a digital signal is widely used which lends good fidelity to the reproduction. Precise equipment is used for synchronization so that satisfactory agreement can generally be attained between the original and the reproduction.